A successful cell phone network requires a large number of continuously operating cell sites. But, there are many situations, natural or man-made, that may affect adversely the continuous operation of a cell site. For example, if some equipment at a cell site is over-heated or even destroyed during the summer, the cell site cannot maintain normal operation and has to be shut down at least temporarily. This situation is very common if the cell site does not install necessary air conditioning units or if the air conditioning units are powered by unreliable utility power and there is not sufficient backup power supply (e.g., backup batteries) at the cell site.
Conventional detection instruments installed at a cell site send monitoring signals to a remote monitoring station when certain predefined conditions are met. But they usually do not have the capability of adjusting automatically the environment of the cell site in response to these conditions, e.g., by switching on a cooling fan or turning off one or more communication channels to lower the temperature inside a building. When an adverse condition occurs, an operator at the monitoring station often has no choice but to shut down the cell site completely until technicians arrives to fix the problems on-site. This approach not only reduces the reliability of the cell phone network but also increases the network carrier's cost.
FIG. 1 is a diagram illustrating a prior art cell site environmental control system, for example, as proposed by companies such as Nextel Communications. This system is used for monitoring and controlling the environment at a cell site so as to improve the reliability of the cell site. For simplicity, FIG. 1 lists only three detectors, AC fault circuit 102, utility power circuit 104 and generator power circuit 106, each circuit coupled to a respective switch circuit, e.g., general-purpose relay or switch, 114, 118 or 122. The closure or opening of a relay or switch indicates a change of state at one particular detector.
The output terminals of the relays are connected to a device that connects one group of wires to another group of wires through a system of metal pegs that the wires are attached, e.g., a punch-down block 110 having multiple rows of terminals. Any state detected by a detector triggers the closure or opening of a corresponding relay or switch, which serves as a monitoring signal. The monitoring signal is transmitted from the relay to the punch-down block 110 and then to a site controller 112 via a cable 111. The site controller 112 then transmits the monitoring signal to a central monitoring station located remotely.
Of course, not every monitoring signal corresponds to an emergency situation that requires the cell site be completely shut down or an immediate technician visit. Some of the adverse conditions can be controlled without a technician visiting the cell site. To do so, the cell site needs to install an automatic environmental control system. According to prior art approaches, another set of general-purpose relays 116, 120 and 124 is installed at the cell site, each coupled to one detector that detects certain changes at the cell site.
The output terminals of the relays are then coupled to a central control module 108. The central control module 108 includes a processor configured to control one or more environmental control devices such as DC load shed systems, air conditioning systems, or exhaust fans (not shown in FIG. 1) to adjust the environment at the cell site in order to maintain a desired environmental condition inside the cell site building. The central control module 108 usually controls these devices through interface modules such as DC load shed control module 130, HVAC control module 132 and fan control module 134.
For example, when the temperature at the cell site rises above a predetermined threshold level, the central control module 108 is triggered to run an algorithm to determine whether to turn on any AC unit and if so, how many active AC units are required to keep the cell site from being overheated. Based on the output of the algorithm, the central control module 108 sends control signals to the HVAC control module 132 to operate accordingly.
There is an output channel 136 between the central control module 108 and the punch-down block 110. This channel allows monitoring signals received by the central control module 108 as well as its processing results to be transferred to the site controller 112 and then to the central monitoring station located remotely.
There are multiple issues with the environmental control system shown in FIG. 1. First, the system requires the installation of an additional set of relays 116, 120 and 124 in order to detect various monitoring signals. Especially in retrofit situations, this requirement significantly increases the system's installation cost. The installation of the additional relays in a retrofit to existing equipment at the cell site, could, for example, void pre-existing safety certifications and manufacturer's warranties. Moreover, a cell site electrical standard usually requires that signal wiring associated with the additional relays be enclosed in metal conduits for equipment safety reasons. Installing these conduits, especially in retrofit situations, could also significantly increase the installation cost for the system. Yet, despite these additional costs, the system in FIG. 1 has so far been the approach adopted by the telecommunication industry.
In view of the above, it is desired to develop a new connection methodology, for the environmental control system, which monitors and controls the environment at a cell site using existing infrastructures.